System and method for processing multiple broadcast multimedia streams

ABSTRACT

A computer-implemented method is disclosed including: receiving a broadcast signal containing a set of multiplexed multimedia channels; storing said multiplexed multimedia channels in a temporary storage buffer on a mass storage device; determining a point in said temporary storage buffer to begin demultiplexing and decoding a first channel responsive to a user request to view a particular program on said first channel in its entirety, said point indicating the start of said program on said first channel; and demultiplexing and decoding said first channel of said set of multiplexed multimedia channels from said point within said temporary storage buffer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/790,076, filed Feb. 20, 2001, which is incorporated by referenceherein in its entirety.

BACKGROUND

1. Field of the Invention

This disclosure relates generally to the field of multimedia systems.More particularly, this disclosure relates to a multimedia systemcapable of intelligently processing and storing several independentbroadcast multimedia streams (e.g., broadcast cable or satellitestreams).

2. Description of the Related Art

A prior art system for receiving broadcast multimedia signals isillustrated in FIG. 1. The system includes one or more tuners 120, 121configured to lock on to multimedia signals 100, 101 transmitted at acarrier frequency and down-convert the signals to baseband signals.Quadrature Amplitude Modulation (“QAM”) demodulators 130, 131 demodulatethe baseband signals to extract the underlying digital content. As isknown in the art, QAM is a modulation technique employed by cable andsatellite providers that generates four bits out of one baud. Forexample, a 600 baud line (600 shifts in the signal per second) caneffectively transmit 2,400 bps using this method. Both phase andamplitude are shaped with each baud, resulting in four possiblepatterns. As indicated in FIG. 1, certain multimedia systems (primarilysatellite systems) use a different modulation technique known asDifferential Phase Shift Keying (“DPSK”) rather than QAM to demodulatethe multimedia signals 100-101.

The video signal demodulated by the QAM/DPSK demodulators 130, 131contains a plurality of statistically multiplexed multimedia streams,each containing content for a single cable or satellite “channel” (e.g.,HBO). Satellite systems employ a series of transponders for receivingthe multiplexed streams and cable systems typically receive themultiplexed streams over 6 Mhz channels. In either case, the multiplexedstreams are transmitted at a combined data rate of approximately 40Mbits/second, as indicated in FIG. 1.

Referring to FIG. 2, each stream/channel may be identified by apredetermined group of packet identification (“PID”) codes. PID filtermodules 140, 141 extract all packets from the set of multiplexed streamshaving PID codes associated with a specified stream (e.g., the streamwhich a user is currently watching). For example, in FIG. 2, PID 7identifies the specified stream's video content and PIDs 5 and 6identify the stream's audio left and audio right, respectively. Variousadditional PIDs may be associated with a stream and used to transmitchannel-specific data/content (e.g., dolby digital content, . . . etc).

The multimedia content contained in the stream is then stored on a massstorage device 160, which may be used for temporary storage and/or longterm storage of the content. Temporary storage features include pauseand rewind functions for live television broadcasts and the ability tobegin watching a program after the designated start time for theprogram. Long term storage functions include the ability to recordentire programs for later viewing (similar to the functions provided bystandard VCR). The multimedia content is then decompressed/decoded byone or more MPEG-2 decoder modules 170 before being rendered on atelevision display 135.

As illustrated in FIG. 1, prior art systems may also utilize a mainmemory 126 for storing instructions and data and a central processingunit (“CPU”) 125 for executing the instructions and data. For example,the CPU may provide a graphical user interface displayed on thetelevision, allowing the user to select certain television or audioprograms for playback and/or storage on the mass storage device 120. Inaddition, prior art system also include one or more conditional accessmodules (not shown) for preventing users from viewing programs whichthey do not have the right to view (e.g., subscription-based channelssuch as HBO and pay-per-view events).

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention can be obtained from thefollowing detailed description in conjunction with the followingdrawings, in which:

FIG. 1 illustrates a prior art multimedia receiver, storage and playbacksystem.

FIG. 2 illustrates packetized, statistically multiplexed multimediacontent as processed by a prior art system.

FIG. 3 illustrates one embodiment of a system for storing and processingmultiple broadcast multimedia streams.

FIG. 4 illustrates an embodiment of a system for storing and processingmultiple broadcast multimedia streams wherein the streams aredemultiplexed before being stored.

FIG. 5 illustrates more detail of an embodiment of a system for storingand processing multiple broadcast multimedia streams wherein the streamsare demultiplexed before being stored.

FIG. 6 illustrates operation of one embodiment which employs a buffer ofa specified duration.

FIG. 7 illustrates an embodiment in which a user may watch any programcurrently being broadcast from the beginning.

FIG. 8 illustrates a graphical user interface for selecting programsfrom a program guide and/or acquiring additional program-relatedinformation according to one embodiment of the invention.

FIG. 9 illustrates a wideband implementation according to one embodimentof the invention.

FIG. 10 illustrates operation of a conditional access module and asecure micro unit.

FIG. 11 illustrates a system for processing multiple multimedia streamsand associated conditional access data.

FIG. 12 illustrates a timestamp index employed in one embodiment of theinvention.

FIG. 13 illustrates techniques for identifying I-frames within amultimedia stream.

FIG. 14 illustrates operation of a fast forward function according toone embodiment of the invention.

FIG. 15 illustrates an embodiment witch includes one or more remotenodes for processing multimedia content.

DETAILED DESCRIPTION

In the following description, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. It will be apparent, however, toone skilled in the art that the invention may be practiced without someof these specific details. In other instances, well-known structures anddevices are shown in block diagram form to avoid obscuring theunderlying principles of the invention.

Embodiments of a System and Method for Processing Multiple BroadcastMultimedia Streams

As illustrated in FIG. 3, one embodiment of the invention includes oneor more tuners 320, 321 for receiving numerous statistically multiplexedstreams within a specified frequency range and corresponding QAM and/orDPSK modules 330, 331 for demodulating the multiplexed streams. Unlikeprior art systems, however, the system illustrated in FIG. 3 transfersall of the statistically multiplexed multimedia content (or a subsetthereof) directly to multi-stream buffers 361, 362 on the mass storagedevice 360. The buffers may be configured to store a specified durationof content (e.g., two hours) and/or a specified amount of content (e.g.,80 Gbytes). When a user selects a particular cable or satellite channel,the PID filter modules 340 and 341 (also referred to herein as a “PIDdepacketizer”) extract the multimedia packets for that channel (i.e.,identified by the channel's PID codes) and reconstruct the underlyingaudio/video content by combining the packets in the proper order (i.e.,the PID filter modules demultiplex and/or depacketize the content). Oneor more decoder modules 170 then decode the multimedia content using theappropriate decode/decompression algorithm (e.g., MPEG-2, MPEG-4,RealVideo® 8, Windows Media Technologies (“WMT”), . . . etc) andtransmit the decoded multimedia content to a display 135 (e.g., acomputer monitor or a television).

As mentioned above, if MPEG-2 is used as the compression algorithm, oneset of multiplexed streams may have a combined bitrate approaching 40Mbits/sec (or 16 Gbytes/hr); two sets, a combined bitrate of 80Mbits/sec (or 32 Gbytes/hr) as indicated in FIG. 3. Accordingly, themass storage device 360 of this embodiment is equipped with sufficientstorage capacity and read-write bandwidth to store and process themultiplexed signal(s). More specifically, the mass storage device 360 inone embodiment is coupled to the system via an Ultra DMA-66/Ultra ATA-66or faster interface (capable of supporting a throughput of at least 528Mbits/sec), and has a storage capacity of 80 Mbytes or greater. Itshould be noted, however, that the particular interface type/speed anddrive storage capacity is not pertinent to the underlying principles ofthe invention. For example, various different interfaces such as SmallComputer System Interface (“SCSI”) may be used instead of theUltra-ATA/Ultra DMA interface mentioned above, and various differentdrive capacities may be employed for storing the incoming digitalcontent.

Storing content from multiple channels/streams on the mass storagedevice 360 in the foregoing manner provides numerous advantages overprior systems. More specifically, one embodiment of the invention usesthe content stored in the multi-stream buffers 360, 361 to provide trickmodes and other short term storage functions for all channels within thestatistically-multiplexed group. For example, if a two-hour multi-streambuffer 361 is established, as indicated in the program guide 600 shownin FIG. 6, a user may pause any channel for up to two hours or rewindany channel back two hours (e.g., at 11:15 PM the user can rewind anychannel back to 9:15 PM). Accordingly, if the user watching Program B onHBO East (PIDs 1-5 in the example) at 11:15, and decides to watchProgram F from the beginning on the HBO Family channel (PIDs 11-15 inthe example), and indicates so by choosing Program F via a remotecontrol device or cursor control device, selection logic 350 will directthe PID filter module 340 to extract Program F from the multi-streambuffer 361. In this manner, the user will be able to view Program F inits entirety even though the broadcast of Program F startedapproximately 1½ hours earlier. Similarly, users may select programs onany of the other channels (e.g., Program L on Cinemax® East) broadcastup to two hours earlier. It should be noted that a two-hour buffer isdescribed above merely for the purpose of illustration. Variousalternate buffer sizes may be employed while still complying with theunderlying principles of the invention.

One embodiment of the invention demultiplexes the incoming multimediastreams before storing them to a multi-stream buffer on the mass storagedevice 460. As illustrated in FIG. 4, this embodiment includes one ormore multi-stream PID filter modules 440, 441 which extract themultimedia streams from the multiplexed signal and store them on themass storage device 460 separated from one another. Thus, as illustratedin greater detail in FIG. 5, if the input to PID filter module 441 is aset of ‘n’ multiplexed streams, then the output will be ‘n’ independent,demultiplexed streams stored in a demultiplexed multi-stream buffer 502.Storage buffers 445, 446 may be used by each of the multi-stream PIDfilters 440, 441, respectively, to construct a portion of each stream(e.g., several Kbytes) before storing the portion to the mass storagedevice 460. This will avoid excessive seeking of the mass storage device460 (e.g., which would result if the storage device 460 were configuredto write a small amount of data such as a single PID packet for eachstream at a time).

Selection logic 550, responsive to a user request to view a particularprogram (e.g., via remote control and/or cursor control device), willdirect the decoder module 171 to read and decode one of the streams(i.e., the streams associated with PIDs 2-3 and 101-102 in the example)for rendering on a television or other display device 136. The sameoperations may be performed on a separate group of ‘m’ multiplexedstreams extracted by multi-stream PID filter module 440.

As indicated in FIG. 5, each of the embodiments described herein mayalso employ a long term storage buffer 500 for recording programsspecified by a user (e.g., similar to the long-term recordingfunctionality of a VCR). In one embodiment, if a user selects a programfor recording while the program is already in progress, the programcontent already stored in one of the demultiplexed multi-stream bufferswill be transferred to the long term storage buffer 500 as well as anynew program content. Alternatively, or in addition, the program contentmay simply be reclassified as long term storage content by changing theclassification of its directory entry on the storage device rather thanmoving the content itself.

One benefit of separating the streams before storing them in theforegoing manner is that, in one embodiment, a user will be able towatch any program currently being broadcast from the beginning (i.e.,the system will record back on each channel to the last completeprogram). Thus, as illustrated in the program guide 500 of FIG. 7, at11:15 a user may watch program N on HBO Signature (PIDs 31-35 in theexample) from the beginning even though the program started at 8:30.Similarly, the user may watch each of programs B, D, F, G, J and F fromstart to finish.

In one embodiment, a user may configure different buffer sizes fordifferent channels. For example, a user who regularly watches a numberof shows on HBO may decide to establish a large (e.g., 6 hour) bufferfor that channel (e.g., by programming the system using a remotecontrol, mouse or other cursor control device), whereas the same usermay configure smaller buffers for channels which the user does not watchregularly (e.g., CSPAN). In one embodiment, the system will activelymonitor the user's preferences and set larger buffer sizes based onwhich channels the user views the most frequently and/or the times/daysduring which the user views the channels. Various other bufferconfiguration schemes may be employed while still complying with theunderlying principles of the invention.

It should be noted that various system functions described herein (e.g.,the selection logic 350, 450, 550 used to select a particular multimediastream; the PID filtering; the buffer settings; . . . etc) may beembodied in software executed by the CPU 125. Alternatively, or inaddition, these functions may be embodied in any combination of hardware(e.g., an application-specific integrated circuit (“ASIC”)), softwareand/or firmware while still complying with the underlying principles ofthe invention.

Using the improved buffering techniques described above, one embodimentof the invention provides users with a listing of all currentlyavailable programs from which they may select (e.g., those programswhich may be viewed in their entirety). As illustrated in FIG. 8, oneembodiment of the program listing is provided in the form of aninteractive graphical user interface (“GUI”). The user may select aparticular program listing by moving a highlight bar 803 through thelistings using a cursor control device such as a remote control,keyboard or mouse. When the highlight bar 803 is highlighting theprogram entry which the user wishes to view, the user may select theprogram entry by clicking the enter key on the keyboard/remote or theselect button on a mouse.

Each program entry in the particular embodiment illustrated in FIG. 8includes a video portion 800 and an informational portion 801. The videoportion in one embodiment is a thumbnail of the actual video contentprovided over the cable/satellite channel. For example, if the firstentry in the program list shown in FIG. 8 is HBO, then the video portion800 of the entry will contain actual HBO video content. As a user movesthrough the various program entries, in one embodiment, the audioassociated with that entry will also be generated. Moreover, in oneembodiment, the system will display various types of user-specifiedbroadcast content including, for example, live content (i.e., theprogram as it is currently being broadcast by HBO), recorded content(e.g., the first few minutes of the movie), or previews of the program(e.g., movie trailers). The underlying principles of the inventionremain the same regardless of the type of content transmitted to thevideo portion 800 of the program entry.

Rendering audio/video content from each of the cable/satellite channelsis simplified using embodiments of the present invention because thefull set of multiplexed streams/channels are transmitted to the massstorage device and are accessible by the decoder modules 170, 171. Sucha configuration was not possible in prior systems which only transmitone or two de-multiplexed streams to the mass storage device and decodermodules.

In one embodiment, a selection region 805 will be provided for eachprogram entry. If a user decides that he/she would like the programentry associated with the selection region 805 to be saved, the user maysimply place a check mark (or other mark) in the selection regioncorresponding to that entry using a remote control or other cursorcontrol device. The system will then store the program in long termstorage and/or reclassify the content as long term content as describedherein. If the embodiment shown in FIG. 3 is employed, one embodiment ofthe invention will depacketize/demultiplex the selected program and savethe program back to the mass storage device 360 (e.g., in either apacketized or a depacketized format). If the user does not wish to viewthe program immediately, this operation may be accomplished as abackground task using the PID filters 340, 341 or other extractionsoftware executed on the CPU 125.

The information portion 801 of the program entry may include varioustypes of program-related data including, for example, the title and yearof the movie (if the program is a movie), program reviews, and/or actorsin the program, to name a few. In one embodiment, the program-relateddata includes links to additional information. For example, the linksmay be network addresses such as uniform resource locators (“URLs”)which point to additional data stored on a network (e.g., the Internet).In response to a user selecting a URL (e.g., via a cursor controldevice), additional data addressed by the URL may be downloaded to thesystem and displayed to the user. Accordingly, this embodiment of thesystem is equipped with a modem or other device for providing two-waycommunication over the Internet or other network (e.g., thecable/satellite provider's network). Various types of modems may beemployed including digital subscriber line (“DSL”) modems, cable modems,and plain old telephone system (“POTS”) dial up modems (i.e., dependingon the particular type of communication channel used by the system). Ofcourse, the type of modem used to support interactive communication isnot pertinent to the underlying principles of the invention.

Wideband Implementations

In one embodiment of the invention, illustrated in FIG. 9, a widebandtuner 910 is configured in to lock on to several groups of multiplexedstreams at once as opposed to just a single group. In the illustratedembodiment, the wideband tuner 910 is comprised of an analog-to-digital(“A/D”) converter 920 for receiving and digitizing numerous incomingstreams—potentially all streams transmitted by a particularcable/satellite provider (e.g., over a 1 GHz frequency range); amulti-pass filter 930 which divides the digitized wideband signal into aplurality of discrete frequency bands (e.g., bands of 100 MHz); and awideband QAM/DPSK module 935 which individually demodulates the contentfrom each of the discrete frequency bands to reproduce all of themultiplexed multimedia streams. In one embodiment, the QAM/DPSK module935 is comprised of a series of digital signal processors (“DSPs”)(e.g., one DSP per frequency band), each programmed with a QAM functionfor performing QAM demodulation and/or a DPSK function for performingDSPK demodulation. In addition, the DSPs may perform other functionssuch as signal equalization and noise filtering. In one embodiment, theDSPs operate under the control of the system's CPU 125 (e.g., the CPDexecutes software comprising the QAM/DPSK functions).

All of the groups of multiplexed streams (which, as indicated in FIG. 9,may include 500 or more PIDs), are transmitted through a wideband PIDselector 940 which, in response to selection logic 450, selects a subsetof all the multiplexed PIDs for storage on the mass storage device 460.The particular number of PIDs selected by the PID selector 940 may varydepending on the preferences of the user and/or the capabilities of themass storage device 460 (e.g., the device's bandwidth and storagecapacity). For example, in one embodiment, users may be prompted toselect a set of “favorite” channels to be continually buffered on themass storage device 460 (whereas the user's non-“favorite” channels willnot be buffered, or will only be buffered for a limited time period). Tosupport the increased storage and bandwidth requirements of the severalsets of additional streams, one embodiment of the invention includes oneor more additional mass storage devices (e.g., connected through amulti-drive high speed communication interface such as UDMA or SCSI).

In one embodiment, a PID demultiplexer 945 demultiplexes/depacketizesthe streams selected by the wideband PID selector before storing them onthe mass storage device 460. Alternatively, or in addition, the streamsmay initially be stored in a multiplexed format on the mass storagedevice and the PID depacketizer 945 may extract PID packets only when auser decides to watch/record a particular program (e.g., as describedabove with respect to the embodiment shown in FIG. 3). Once selected bya user, the stream is then transmitted through a decoder module 170 forMPEG-2 decoding (or other type of decoding, depending on how the streamwas initially encoded) and to a display 135. Although illustrated aboveas two separate modules, it will be appreciated that the functionalityof the PID demultiplexer 945 and wideband PID selector 940 may becombined within a single module.

In one embodiment, a separate set of analog modules 911 may be includedin the system to process and store legacy analog broadcasts. The analogcomponents may include an analog tuners 902 for receiving the analogbroadcast at a particular frequency, a decoder/digitizer module 904 fordecoding and performing A/D conversion on the analog signal, and acompression module 906 for compressing the signal before storing it tothe mass storage device 460.

In one embodiment, the digital components may be configured to providethe analog functionality just described. For example, the DSPs withinthe QAM/DPSK module 935 may be programmed with an NTSC or PALdemodulation function for demodulating the incoming analog signal 901(i.e., after the signal is digitized via the A/D converter).

Conditional Access Embodiments

In order to prevent users from viewing multimedia content which they donot have the right to view (e.g., subscription based channels,pay-per-view channels, . . . etc) the multimedia content is frequentlyencrypted using a series of encryption keys before being transmitted.Accordingly, multimedia systems are generally equipped with conditionalaccess (“CA”) subsystems for decrypting the incoming multimedia content.

FIG. 10 illustrates a CA module 1010 decrypting an incoming multimediastream 1030 to produce a decrypted multimedia stream 1035, which is thendecoded by decoder 170 (e.g., using an MPEG-2 decoder) and rendered on atelevision display 135. The decryption keys 1025 used to decrypt themultimedia content are transmitted to the CA module 1010 from a securemicro unit 1020. Because the keys used to encrypt the multimedia streamtypically change every few seconds, these key changes must besynchronized at the secure micro 1020 and CA modules 1010. Accordingly akey selection data stream 1040 (also referred to herein as the “PID:CA”stream or “conditional access data”) is provided to the secure microunit 1020 so that it knows precisely which key to transmit to the CAmodule 1010 at a given point in time.

As a result of the CA subsystem, if the incoming multimedia stream isstored in an encrypted format on a mass storage device, the decryptionkey changes associated with that multimedia stream must also be stored(i.e., so that when a user selects the stream, the secure micro willprovide CA module with the decryption keys required to decrypt thestream). Prior systems deal with this problem simply by decrypting themultimedia stream before it is stored. However, storing decryptedcontent on a long term storage device in this manner leaves thecopyright holder of the content exposed to unauthorized copying. Inaddition, because CA subsystems are typically only capable of decryptingone stream at a time, this configuration only provides for storage ofonly a single stream per CA module.

One embodiment of a system for concurrently processing decryption keysfor multiple streams is illustrated in FIG. 11. Like prior embodiments,this embodiment includes one or more tuners 1020, 1021 for locking on tomultimedia stream within a specified carrier frequency and one or moreQAM and/or DPSK demodulators 1030, 1031 for demodulating the multimediastream.

Unlike prior systems, however, the illustrated embodiment stores thePID:CA key selection data 1145 identifying the keys 1146 to be suppliedby the secure micro 1160 to the CA modules 1170, 1171 for eachmultimedia stream, as well as timing data indicating the points in timeat which each portion of the multimedia stream and associated keyselection data 1145 were received/stored on the system (oralternatively, the points in time at which the stream/content wastransmitted). When a user subsequently chooses a particular multimediastream for playback, the secure micro 1160 uses the key selection dataPID:CA 1145 for that stream to provide the correct series of keys to theCA modules 1170, 1171 for decryption of the selected stream. As in theembodiments described above, the user may be able to watch any programstored on the mass storage device for a predetermined buffer period orfrom the beginning (e.g., as described above with respect to FIGS. 6 and7, respectively). In one embodiment, stream selection logic 1155(embodied in hardware or software executed by the CPU 1185) will selectthe correct multimedia stream and PID:CA stream at the correct point intime (e.g., using techniques described in greater detail below)responsive to the user's selection (e.g., via a remote control or acursor control device). Once the multimedia stream is decrypted by oneof the CA modules 1170, 1171, one or more decoder modules 1180 thendecode the stream using an appropriate codec (e.g., MPEG-2) and transmitthe decoded stream to a display 135.

Identifying the correct points in time within the multimedia stream tobegin playback is complicated by the fact that MPEG-2 data (as well asother types of encoded multimedia content) is not typically received bythe system at a steady rate. For example, a portion of an MPEG-2 streamwhich contains significant movement between each of the image frames(e.g., a video of an explosion) will typically consume significantlymore bandwidth than a portion of an MPEG-2 stream that contains littleor no movement. Thus, as illustrated in FIG. 12, four 1-second portions(1211, 1212, 1213, 1214) of the incoming multimedia stream 1210 mayoccupy different amounts of space on the mass storage device. As such,in one embodiment of the system, an index of timing data 1200 isprovided so that the stream selection logic 1155 can accurately locatewhere on the hard drive to start decrypting/rendering the multimediastream in response to a user request to play back a particular program.Included within the index 1200 is a series of address pointers1201-1204, each associated with a timestamp (labeled 8:00:00 through8:00:03). In operation, if a user selects a stored program which startedat 8:00, for example, the stream selection logic 1155 will identify the8:00:00 timestamp within the index 1200 and will startdecrypting/playing the program stream back from the address identifiedby pointer 1201.

In one embodiment, the stream selection logic 1155 will also identifythe appropriate point within the PID:CA stream from which to read thenecessary key changes. In one embodiment, a separate set of pointers tothe PID:CA stream may be included within the timestamp index 1200 or,alternatively, within a separate PID:CA index (not shown).Alternatively, the conditional access data PID:CA may be stored directlywithin the index 1200. However, in an embodiment in which the PID:CAstream is not encrypted and/or is transmitted at a steady rate (e.g.,0.1 Mbit/sec), address pointer entries to the PID:CA stream may not berequired (i.e., the selection logic will be able to accurately identifywhere to read from the PID:CA stream without the need for an index).

In one embodiment, the timing index 1200 is transmitted along with themultiplexed multimedia streams in the form of an additional PID stream(e.g., a PID:INDEX stream transmitted from the head-end or uplinksatellite that feeds the head-end). In other words, in this embodiment,the organization providing the source material (e.g., the cable orsatellite provider) will generate and transmit the index to the enduser's system.

However, if the content provider does not transmit the index, oneembodiment of the system will construct the index 1200 as the multimediastreams are received and written to the mass storage device. Forexample, index/timestamp generation logic executed by the CPU 1185 (orembodied in hardware) may be configured to generate a new timestampentry every 1/100 of a second and continuously store the results to themass storage device 1140. However, it should be noted that theparticular frequency with which timestamp entries are generated is notpertinent to the underlying principles of the invention.

As illustrated in FIG. 13, an MPEG-2 stream 1310 is comprised of aseries of I-frames separated by B-frames and P-frames. MPEG-2 usessimilar DCT-based intraframe coding as the JPEG standard for each of theI-frames, but compresses the intervening video content by encoding onlythe differences between periodic I-frames within the B-frames andP-frames. Accordingly, it would be preferable if the pointers 1201-1204contained in the timestamp index 1200 pointed to I-frames within theMPEG-2 stream rather than B or P frames (i.e., because the B and Pframes are meaningless outside of the context of the two I-frames theyconnect). Accordingly, if the timestamp index is generated by theorganization providing the source material, each of the pointers1201-1204 should be selected to point to I-frames within the MPEG-2stream.

If, however, the timestamp index 1200 is generated by the system, asdescribed above, then the pointers 1201-1204 may not necessarily pointto an I-frame. Accordingly, in one embodiment of the invention, if astream is played back from an address pointer which does not point to anI-frame (e.g., such as pointer 1201 in FIG. 13) then it willdecrypt/decode the stream up until it reaches an I-frame and will beginplayback from that point. For example, in FIG. 13, the system will begindecrypting the stream at the point identified by pointer 1201 (in themiddle of B & P frames 1302) but playback would not start until thedecryption process reached I-frame 1303. In one embodiment, the systemidentifies the I-frame 1303 by decrypting its I-frame header.

Similar techniques may also be employed to allow users to fast-forwardthrough the multimedia content. More specifically, in response to a fastforward command, one embodiment of the system will display a series ofI-frames in succession. Depending on the speed at which the fast forwardis set to, this embodiment may jump several I-frames at once (asdescribed in greater detail below). If the timestamp index describedabove contains pointers which point directly I-frames, then the I-frameswill be identified directly via the index.

If, however, the index is constructed as the multimedia stream isreceived, then jumping from one I-frame to the next may not be entirelyaccurate because the number of B and P frames between each I-frame andthe data contained within each B and P frame is not consistent.Accordingly, as illustrated in FIG. 14, when a user selects fastforward, one embodiment of the system will estimate the jump from thecurrent I-frame 1301 to the next I-frame 1303 based on the speed of fastforward request and/or the estimated time between each I-frame. In oneembodiment, the system will perform a lookup in the timestamp index 1200to make the jump. Alternatively, or in addition, the jump may be basedon the assumption that during standard playback, a new I-frame isdecided approximately every ½ second. The underlying principles of theinvention remain the same regardless of how the jump to the next I-frameis estimated.

Regardless of how the jump is estimated, once it occurs, one embodimentwill then begin decrypting the stream using the decryption key dataPID:CA 1145 associated with that point in time, until the decryptionprocess reaches the desired I-frame 1303. Once the I-frame 1303 isreached, it is decrypted, decoded and rendered on the display. The sametechniques may then be employed for the estimated jump to the nextI-frame 1305. The system may identify each of the I-frames by decryptingtheir respective I-frame headers.

If one embodiment, if the jump lands in the middle of the next I-frameas illustrated in FIG. 14 (as the jump from I-frame 1305 to 1307, thenone embodiment of the invention will decrypt the stream backwards untilit reaches the beginning of I-frame 1307. The system may identify themiddle of an I-frame by the presence of I-frame data rather than B or Pframe data (e.g., DCT intra-frame data rather than inter-frame motiondata).

If the speed of the fast forward request is set high enough the securemicro unit 1160 may be required to provide a new decryption key witheach jump. Accordingly, one problem which may result is that the securemicro 1160 may not be capable of providing decryption keys to the CAmodule 1170 quickly enough (e.g., the secure micro may only be capableof supplying a new key every ⅓ second). If this is the case, then oneembodiment of the invention will continue to display the current I-frameuntil a new key can be generated as it jumps over several I-frames at atime. In this manner, decryption will take place as quickly as thesecure micro unit 1160 can generate new keys.

As the multimedia stream is decrypted during playback, one embodiment ofthe invention will store the decrypted stream back to the mass storagedevice 1140, thereby replacing the encrypted multimedia data. At thistime an I-frame index can be written to the storage device 1140 as well.Accordingly, if a user subsequently decides to rewind to a particularpoint within the multimedia stream, or decides to watch the program asecond time, the foregoing I-frame identification techniques may nolonger be required (i.e., because the stream will have been decryptedand an I-frame index may be available). In addition, in one embodiment,as soon as the user begins watching a particular multimedia stream, thesystem will run ahead of stream playback, decrypting the stream asquickly as it can (generally dictated by how quickly the secure microunit 1160 can supply keys) and storing the decrypted stream back to themass storage device. Using this technique an entire movie may becompletely decrypted during the first several minutes of playback.Accordingly, if the user subsequently chooses to fast-forward throughthe movie, the I-frame identification techniques described above willnot be required.

In one embodiment, any multimedia programs which the user designates forlong term storage (e.g., by checking the selection region 805corresponding to the program as illustrated in FIG. 8), will bedecrypted in the background by software executed on the CPU 1185 and/orusing dedicated decryption hardware. This embodiment may be required incases where the decryption keys provided by the cable/satellite providerexpire after a predetermined period of time (i.e., and therefore couldnot be used to decrypt the multimedia programs after a predeterminedtime has elapsed).

In order to protect the copyright holders' rights in the multimediacontent stored on the mass storage device 1140, one embodiment of theinvention will employ additional encryption techniques once themultimedia content has been decrypted. For example, one embodiment ofthe system delivers a unique key to the mass storage device 1140 as soonas the system is powered up. This technique is available today on manycurrent Ultra-ATA hard drives. If the wrong key is transmitted apredetermined number of times, the hard drive will render the datastored thereon inaccessible (e.g., in one embodiment the hard drive willformat itself). Accordingly, an individual who steals the mass storagedevice 1140 will be unable to access the multimedia content.

In addition, in one embodiment, after the multimedia content isdecrypted using keys supplied by the secure micro 1160, one embodimentwill re-encrypt the content using one or more known encryptionalgorithms. For example, in one embodiment, Data Encryption Standard(“DES”) encryption will be applied to the multimedia content beforestoring it back to the mass storage device 1141. As is known in the art,DES is a NIST-standard secret key cryptography method that uses a 56-bitkey. It will be appreciated, however, that various other encryptionalgorithms may be employed while still complying with the underlyingprinciples of the invention. However, one benefit of using DESencryption is that many MPEG-2 decoder chips have the DES encryptionfunction built in (e.g., such as the AViA-9600 from C-Cube Microsystems,Inc). As such, if the system is equipped with an MPEG-2 decoder, noadditional hardware will be required, thereby reducing system costs.

In one embodiment, illustrated in FIG. 15, a network interface 1500 isconfigured in the system to provide communication to a remote multimedianode 1510 (also equipped with a network interface 1505). Variousdifferent networking protocols/standards, both wired (e.g., Ethernet)and wireless (e.g., 802.11b), be employed to support the communicationbetween the various nodes.

The format in which multimedia content is transmitted to the multimedianode 1510 may depend on the node's capabilities. For example, in oneembodiment, the node 1510 is equipped with its own conditional accessmodule and secure micro unit (not shown). Accordingly, in thisembodiment, multimedia streams requested by the remote node 1510 may betransmitted in an encrypted format along with the associated keyselection data PID:CA. By contrast, in one embodiment the remote node1510 may not be equipped with conditional access functionality. As such,in this embodiment, the multimedia content will be decrypted beforebeing transmitted. In order to protect unauthorized access to themultimedia content (e.g., by an unauthorized user listening on thenetwork), one embodiment will re-encrypt the stream before transmittingit to the remote node 1510 using an encryption format which the remotenode can employ in real time (e.g., DES encryption). Various othertechniques may be used to provide secure communication with the remotenode 1510 while still complying with the underlying principles of theinvention (e.g., communication may be encrypted using Secure SocketsLayer (“SSL”) encryption).

Embodiments of the invention may include various steps, which have beendescribed above. The steps may be embodied in machine-executableinstructions which may be used to cause a general-purpose orspecial-purpose processor to perform the steps. Alternatively, thesesteps may be performed by specific hardware components that containhardwired logic for performing the steps, or by any combination ofprogrammed computer components and custom hardware components.

Elements of the present invention may also be provided as a computerprogram product which may include a machine-readable medium havingstored thereon instructions which may be used to program a computer (orother electronic device) to perform a process. The machine-readablemedium may include, but is not limited to, floppy diskettes, opticaldisks, CD-ROMs, and magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs,magnet or optical cards, propagation media or other type ofmedia/machine-readable medium suitable for storing electronicinstructions. For example, the present invention may be downloaded as acomputer program product, wherein the program may be transferred from aremote computer (e.g., a server) to a requesting computer (e.g., aclient) by way of data signals embodied in a carrier wave or otherpropagation medium via a communication link (e.g., a modem or networkconnection).

Throughout this detailed description, for the purposes of explanation,numerous specific details were set forth in order to provide a thoroughunderstanding of the present invention. It will be apparent, however, toone skilled in the art that the system and method may be practicedwithout some of these specific details. For example, although thedescription above focuses on MPEG-2 as the preferred compressionalgorithm, various other compression algorithms may be employed tocompress/decompress multimedia content while still complying with theunderlying principles of the invention (e.g., MPEG-4, RealVideo® 8, . .. etc).

In other instances, well known structures and functions were notdescribed in elaborate detail in order to avoid obscuring the subjectmatter of the present invention. For example, although not illustrated,it will be appreciated that various levels of buffering may be includedin the embodiments described herein. For example, in the embodimentillustrated in FIG. 11, buffers (e.g., SDRAM, RDRAM, . . . etc) may beconfigured between the QAM/DPSK modules 1130, 1131 and the mass storagedevice 1140 and/or between the mass storage device 1140 and the PIDfilters 1150, 1151. In fact, buffers may be provided in this mannerbetween any of the system modules in order to improve systemperformance. The buffers may be separate, independent modules and/or maybe assigned blocks of addressable space within a single unified memory(e.g., a RAM module shared between the CPU 1185 and other systemcomponents). The underlying principles of the invention remain the sameregardless of which types of buffers are used.

Accordingly, the scope and spirit of the invention should be judged interms of the claims which follow.

1. A method comprising: receiving a broadcast signal at a set top box containing a set of multiplexed multimedia channels, the set top box including a temporary storage buffer on a mass storage device; storing said multiplexed multimedia channels in the temporary storage buffer on the mass storage device; if the multiplexed multimedia channels stored on the mass storage device are encrypted, storing a plurality of encryption keys respectively associated with portions of the multimedia channels stored on the mass storage device and timing data associated with the plurality of encryption keys; determining a point in said temporary storage buffer to begin demultiplexing and decoding a first channel from said multiplexed multimedia channels received at the set top box, said determining being performed responsive to a user request to view a particular program on said first channel, said point indicating the start of said program on said first channel without receiving a user request to return to the beginning of the particular program; retrieving encryption keys from the mass storage device based upon the point indicating the start of said program; and demultiplexing and decoding and decrypting said first channel of said set of multiplexed multimedia channels received at the set top box using the retrieved encryption keys, the demultiplexing and decoding and decrypting being performed from said point within said temporary storage buffer.
 2. The method as in claim 1 wherein each multimedia channel in said set is comprised of packets of multimedia content.
 3. The method as in claim 2 wherein said packets are identified as containing data for a particular multimedia channel by way of a unique packet identification (“PID”) code.
 4. The method of claim 1, wherein determining said point in said temporary storage buffer comprises: receiving with said multiplexed multimedia channels an index comprising a pointer to an address within said multiplexed multimedia channels to begin demultiplexing and decoding said first channel in order to view said program.
 5. The method of claim 1, wherein determining said point in said temporary storage buffer comprises: generating, as said multiplexed multimedia channels are received, an index comprising a pointer to an address in said multiplexed multimedia channels to begin demultiplexing and decoding said first channel in order to view said program.
 6. The method as in claim 1 wherein said buffer is configured to store a specified block of time of said multiplexed multimedia channels.
 7. A set top box system comprising: tuning means to receive a broadcast signal containing a set of multiplexed multimedia channels from a cable or satellite service provider; storage means to store said multiplexed multimedia channels in a temporary storage buffer on a mass storage device and if the multiplexed multimedia stream is encrypted, to store a plurality of encryption keys associated with the multiplexed multimedia channels and timing data associated with the plurality of encryption keys; and selection means to select a first channel of said multiplexed multimedia channels in said set stored on said mass storage device responsive to a user request to view multimedia content contained in said first multimedia channel; playback point determination means for determining a point in said temporary storage buffer to begin demultiplexing and decoding said first multimedia channel responsive to a user request to view a particular program on said first multimedia channel, said point indicating the start of said program on said first multimedia channel without receiving a user request to return to the beginning of the particular program; selecting an encryption key from among the plurality of encryption keys, the selection being based upon the point determined by playback point determination means; and demultiplexing and decoding and decryption means to demultiplex and decode and decrypt said first channel from said point within said temporary storage buffer using the selected encryption key and subsequent keys respectively associated with subsequently retrieved portions of the particular program.
 8. The system as in claim 7 wherein each multimedia channel is comprised of packets of multimedia content.
 9. The system of claim 7, further index generation means to generate, as said multiplexed multimedia channels are received, an index comprising a pointer to an address in said multiplexed multimedia channels to begin demultiplexing and decoding said first channel in order to view said program.
 10. The method as in claim 7 wherein said buffer is configured to store a specified block of time of said multiplexed multimedia channels.
 11. The method as in claim 7 wherein said buffer is configured to store a specified amount of multimedia content.
 12. A system for processing a plurality of multimedia channels comprising: a tuner to receive a broadcast signal at a specified frequency and convert said broadcast signal to a baseband signal; a demodulator to demodulate said baseband signal to produce a plurality of multiplexed multimedia channels; a mass storage device for storing said set of multiplexed multimedia channels and for storing a plurality of encryption keys respectively associated with segments of the multiplexed multimedia channels; selection logic for selecting one of said multiplexed multimedia channels stored on said mass storage device to render on a display responsive to a user command and for determining a point in said set of multimedia channels to begin demultiplexing said selected multimedia channels responsive to a user request to view a particular program within said selected multimedia channel, said point indicating the start of said program without receiving a user request to return to the beginning of the particular program; a secure micro component operable to select an encryption key from the plurality of encryption keys based on the selected point in the selected multimedia channel; and a multi-channel PID filter module to demultiplex said selected multimedia channel prior to decrypting and rendering said selected multimedia channel on said display from said beginning point.
 13. The system as in claim 12 wherein each of said multimedia channels are logically separated into a series of programs.
 14. The system as in claim 13 wherein said multi-channel PID filter continues to store a first program on a first multimedia channel of said set of multiplexed multimedia channels as long as said first program on said first multimedia channel is being broadcast by a cable or satellite provider.
 15. The system as in claim 14 wherein said first program is deleted from said mass storage device when said cable or satellite provider stops broadcasting said first program.
 16. The system as in claim 15 wherein said multi-channel PID filter begins storing a second program of said first multimedia channel to said mass storage device responsive to said cable or satellite provider transmitting said second program.
 17. The system as in claim 14 wherein, responsive to a user request to view said first program on said first multimedia channel, said selection logic selects said first program to be decoded and rendered on said display from the start of said first program.
 18. The system as in claim 12 further comprising: a long term storage buffer configured on said mass storage device for recording one or more of said multimedia channels for an indefinite period of time responsive to a user request to record said one or more programs.
 19. The system as in claim 12 further comprising: a graphical user interface displaying a list of program entries from which a user may select, said program entries corresponding to one or more entire programs transmitted within said set of multiplexed multimedia channels.
 20. The system as in claim 19 wherein said graphical user interface further comprises selection regions associated with each of said program entries and wherein, responsive to a user selection of one or more of said selection regions, said programs associated with said selection regions are stored in a long term storage buffer configured on said mass storage device.
 21. The system as in claim 19 wherein said program entries include a video portion for displaying a video relating to said one or more programs.
 22. The system as in claim 21 wherein said program entries further include an information portion for displaying information related to said one or more programs.
 23. The system as in claim 22 wherein said information portion is comprised of one or more uniform resource locators (“URLs”).
 24. The system as in claim 21 wherein said program entries are grouped into one or more categories.
 25. The system of claim 12, wherein said selection logic is further to receive with said set of multiplexed multimedia channels an index comprising a pointer to an address in said set of multiplexed multimedia channels to begin demultiplexing and decoding said first multimedia channel in order to view said program.
 26. The system of claim 12, further comprising index generation logic to generate, as said multiplexed multimedia channels are received, an index comprising a pointer to an address in said multiplexed multimedia channels to begin demultiplexing and decoding said first multimedia channel in order to view said program.
 27. A set top box system comprising: a wideband tuner to receive two or more groups of multiplexed multimedia channels at a plurality of specified frequency ranges; a wideband demodulator to demodulate said two or more groups of multiplexed multimedia channels; a mass storage device to store said two or more groups of multiplexed multimedia channels including a plurality of encryption keys respectively associated with segments of the two or more groups of multiplexed multimedia channels; a wideband multi-channel PID filter module to filter certain multimedia channels from said two or more groups of multimedia channels; and selection logic for selecting one or more of said filtered multimedia channels to render on a display, wherein said selection logic is further to determine a point in said mass storage device to begin decoding a first channel responsive to a user request to view a particular program on said first channel, said point indicating the start of said program on said first channel without receiving a user request to return to the beginning of the particular program; a secure micro component operable to select an encryption key from among the plurality of encryption keys based upon a segment of the particular program identified by the selection logic.
 28. The system as in claim 27 wherein a first channel of said filtered channels is logically separated into a series of programs.
 29. The system as in claim 28 wherein said wideband multi-channel PID filter continues to store a first program of said first channel to said mass storage device as long as said first program in said first channel is being broadcast by a cable or satellite provider.
 30. The system as in claim 29 wherein said first program is deleted from said mass storage device when said cable or satellite provider stops broadcasting said first program.
 31. The system as in claim 30 wherein said wideband multi-channel PID filter begins storing a second program to said mass storage device responsive to said cable or satellite provider transmitting said second program.
 32. The system as in claim 29 wherein, responsive to a user request to view said first program, said selection logic selects said first program to be decoded and rendered on said display from the start of said first program.
 33. The system as in claim 28 further comprising: a long term storage buffer configured on said mass storage device for recording one or more programs for an indefinite period of time responsive to a user request to record said one or more programs.
 34. The system as in claim 27 wherein said two or more groups of multiplexed multimedia channels comprise all channels broadcast by a cable or satellite provider. 